The invention relates generally to the field of power electronic devices such as those used in power conversion or applying power to motors and similar loads. More particularly, the invention relates to an improved system and method of utilizing a pre-charge circuit in an inverter module such as a motor drive.
In the field of power electronic devices, a wide range of circuitry is known and currently available for converting, producing and applying power to loads. Depending upon the application, such circuitry may convert incoming power from one form to another as needed by the load. In a typical motor control, for example, a rectifier converts alternating current (AC) power (such as from a utility grid or generator) to direct current (DC) power. Inverter circuitry can then convert the DC signal into an AC signal of a particular frequency desired for driving a motor at a particular speed. The inverter circuitry typically includes several high power switches, such as insulated-gate bipolar transistors (IGBTs), controlled by drive circuitry. Often, power conditioning circuits, such as capacitors and/or inductors, are employed to remove unwanted voltage ripple on the internal DC bus.
Often, at the first application of AC power to the motor drive circuit detailed above, the circuit will draw high levels of current due to the charging of the power conditioning capacitors. Therefore, to avoid a high in-rush current at start-up, a typical motor drive may also include a pre-charge circuit, which applies a smaller initial current to the DC bus just prior to start-up to charge the capacitors before a full source voltage is applied.
Typically, the motor drive circuitry detailed above, including the pre-charge circuit, may be packaged together as a motor drive module. To reduce manufacturing costs, motor drive modules are mass produced and are, therefore, available in the form of standardized product lines. Often, this means that the capabilities of the motor drive may not be fully utilized, depending on the particular application. For example, it may be desirable in a particular power control network to couple several motor drives to a common DC source. In this example, the common DC source may be coupled directly to the local DC bus of the motor drive module, by-passing the rectifier and the pre-charge circuit, which will, therefore, go unused. It may also be desirable, however, to include an operable pre-charge circuit for each individual motor drive, in which case additional pre-charge circuits may need to be added to the power control network, because the existing pre-charge circuit of the motor drive may not be accessible due to the wiring of the common DC source to the local DC bus. This added pre-charge circuitry adds cost to the overall design of the power control network.
Therefore, it may be advantageous to provide an inverter module that is more adaptable. In particular, it may be advantageous to provide an inverter module with an improved method for utilizing the pre-charge circuit in various modes of operation.